Touring - add-on side supports on a rear rack feasibility

Not sure if this is the appropriate forum, but I'm currently prepping for a solo, southern tier coast-to-coast ride that I'm embarking on in May. Like my last little tour, this will be on a tight budget, though more practical than the 50 dollars i had last time.

I confidently plan on using my cheapo schwinn rear rack that does not have pannier supports, and this is because I'm riding my rebuilt schwinn varsity 08 (the cheap wal mart one). This frame has no holes by the rear wheel mount for a traditional rear rack, and I fully intend on using this frame for the trip. My question is, are there pannier-supporting side bars I can add on, and if not, what is the risk and feasibility of just making one out of parts from a hardware store, that may include drilling through or screwing into the aluminum frame?

Aluminum stock and some hardware can cost almost as much as buy an inexpensive pannier rack.

Use P-clamps to attach stuff to your frame. Holes in an aluminum frame will tend to fatigue crack.

Is the schwinn rack one of those that only attaches to the seatpost? Is this what you mean by lacking pannier supports? I've seen people use coroplast (the stuff election signs are made of) as a backing for panniers. (or even as panniers themselves) Any metal strapping, rod, flat stock, etc you could run from the rack down to a P-clamp would work too. Heck, coat hangar wire might work. Just don't expect it to do anything but keep the panniers out of your wheel. Do you know if your rack can hold however much you're planning on bringing?

Do you have a bike co-op in your area that might have a used rack for sale? Maybe try posting on craigslist, check out garage sales, salvation army, etc.

If you can weld steel, you can build some racks for your bicycle. I built both of mine for $10. That is the front and rear rack. I got some 5/16 cold rolled solid stock, 20 foot joint, and some 1/4 inch nuts to use for the braze ons. The front rack you can use some small U bolts to clamp the rack to the fork or use hose clamps. I did that for my trek, but I upgraded to a Randonee, so I had to modify the front rack to use the braze ons.

Thank you for the replies! All very helpful info too. Now I can't weld, and now knowing that machining aluminum may be expensive, this p-clamp idea sounds pretty awesome. I'll do that to stabilized the panniers from touching the wheel, as well as add some vertical support to the solely horizontally mounted rack. thanks.